Various ignition coils have been proposed for generating sparks from the spark plug of an internal combustion engine. For example, FIGS. 20 and 21 show a conventional stick type ignition coil 9 for an engine of a car or other vehicle. The ignition coil 9 has a cylindrical body 92 and an igniter head 93. The cylindrical body 92 is inserted in the plug hole of the engine case 8 and fitted with a primary coil and a secondary coil that are coaxial with each other. The igniter head 93 is coupled to one end of the cylindrical body 92 and supplies the primary coil with power.
The igniter head 93 has a connector 933, which is connected electrically to an engine control unit (i.e., ECU) outside the ignition coil 9. The connector 933 includes a connector pin 952 for the battery (i.e., plus power supply), a connector pin 951 for grounding (i.e., minus power supply), and two connector pins 953 for transmission of a control signal. The igniter head 93 also has a casing 931 and a flange 932, which protrudes from the casing 931. The ignition coil 9 is coupled to the engine case 8 by means of the flange 932.
The connector pin 951 for grounding is connected electrically to the engine case 8 so that electrical noise can be reduced. Once electrically connected, the ground in the ignition coil 9 should be at the same potential as the ground in the engine case 8.
Therefore, as shown in FIGS. 20 and 21, the ignition coil 9 has a ground terminal 94, which includes the connector pin 951 for grounding, an annular contact 97 and a connecting part 96. The annular contact 97 is included on one face of the flange 932 so as to abut the engine case 8. The connecting part 96 connects the connector pin 951 and the annular contact 97. The connector pin 951 for grounding is electrically connected (i.e., short-circuited) to the fitting part 82 of the engine case 8 via the connecting part 96 and the annular contact 97.
Typically, the ground terminal 94 is insert-molded in the casing resin material 930 that forms the casing 631. The casing resin material 930 is typically a thermoplastic resin because it is highly moldable. However, because of this material, the resin 930 can release from the ground terminal 94. Consequently, for example, gaps may exist between the casing resin 930 and the ground terminal 94. The gaps may develop over time, for instance, due to temperature changes that occur during the operational life of the ignition coil 9.
As shown in FIG. 20, if moisture S reaches the flange 932, the moisture S may pass through the gaps between the casing resin 930 and the ground terminal 94 and travel from the annular contact 97, along the connecting part 96, and to the connecting pin 951 for grounding. In this case, the water S may cause a short circuit (i.e., an insulation failure) between the connecting pin 951 and one of the other connector pins 952, 953 and/or corrode (i.e., rust) the connecting pin 951. Also, a contact failure (i.e., a conduction failure) may occur between the corroded pin 951 and the socket to which the connector pins 951-953 are connected.
U.S. Pat. No. 5,433,628 (Japanese Patent No. 6-84565A) discloses a sealing structure in which a connector is molded integrally with a connector housing. Part of a terminal of the connector is embedded in the wall of the connector housing through a seal coating material. As such, water and/or oil is unlikely to intrude from the connector terminal into the connector housing.
However, the device of U.S. Pat. No. 5,433,628 uses a seal coating material to limit the intrusion of water and/or oil. Thus, the construction of the device is relatively complex.